The crux of the issue seems to be a quote from a Huffington Post interview with US Air Force Colonel Michael Valle, reports Snopes.

Valle said: “Supplies we have. Trucks we have. There are ships full of supplies backed up in the ports, waiting to have a vehicle to unload into. However, only 20% of the truck drivers show up to work.”

The main reason for the shortages is that local truck drivers have been displaced and are difficult to contact, due to fallen power lines. Puerto Rico is also dealing with blocked roads and diesel fuel shortages.

On Monday, the Teamsters Union clarified that union workers have been contributing to delivery efforts “since day one” and that unions are sending more truckers from across the US to help out. Additionally, a Puerto Rican government representative told CBS that claims were false, and that drivers are increasingly able to drive to ports to pick up necessary supplies.